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Temperature Effects on Sea Turtle Sex Ratios and the Potential Impact of Climate Change

Sea turtle hatchlings.

Photo by Kate Shaffer.

Admittedly, I know very little about sea turtles. After starting my internship at the National Marine Life Center I decided to order a book specifically dedicated to the biology and behavior of these mysterious oceanic reptiles. One interesting fact I came across while reading was that the temperature at which the eggs are incubated determines whether or not the turtle will be male or female.Most vertebrates have sex chromosomes (XX for female and XY for male), however, sea turtles lack these chromosomes.

Females need warmer temperatures in order to develop. For example, in green turtles, temperatures need to be 88 F or above for the eggs to become females. For males to develop the temperature is around 82 F. If the temperature of incubation falls somewhere between 82 and 88 F, a mixture of the sexes develop. Heat produced by the eggs themselves can also contribute to the incubation temperature – eggs in the center of the nest become females and the eggs along the periphery become males (Spotila 2004).

If temperature affects the sex ratio of sea turtles, how might climate change impact populations in the future? Currently, sea turtle populations that nest in the southern portion of the United States are predominately female biased. It has been suggested (Hawkes 2007) that if there is even a 1 C warming of average temperatures, an even more significant bias could occur. If average warming exceeds 3 C, mortality rates of the eggs may also occur.

Climate change may also affect the nesting grounds of turtles if sea levels rise. Beaches currently being used by turtles may vanish under the sea. Ocean acidification (caused by increased CO2 levels) could potentially alter the sediment of the beaches, which may lead to inadequate conditions for incubation (Fuentes et al 2011). Sea turtles select their nesting sites based on several factors, such as low salinity, sufficient space above the hide tide line, adequate vegetation (for some species), high humidity, etc (Hawkes 2007). All of these may be affected by an increase in average global temperatures.

Future studies need to be conducted to better estimate the current sex ratios of the various sea turtle species in order to better predict how these will be affected by changes in nesting/incubation environments. Some possible ways that sea turtles may prevent extremely biased female sex ratios are by nesting earlier (cooler periods), nesting at higher latitudes (more north), changing the depth at which they bury their eggs, or changing the type of substrate they bury their eggs in (i.e. type of sand). That way more eggs will develop into males that might have otherwise been females (Fuentes 2011).

Just recently (August 18 2011), the first sea turtle nest was discovered in Delaware. Sea turtles are not known to nest that far north as well as that late in the season. They typically lay their nests on the coasts on South Carolina, Georgia and Florida. Alex Hoar, the U.S. Fish & Wildlife Service’s Northeast Endangered Species Coordinator said that, “And with global warming, events such as this may be a sign of what is to come” (Delaware Online).


Fuentes M.M.P.B, Limpus C.J., Hamann M. 2011. Vulnerability of sea turtle nesting grounds to climate change.  Global Change Biology. 17(140-153)

Hawkes L.A., Broderick A.C., Godfre M.H, Godley B.J. 2007. Investigating the potential impacts of climate change on a marine turtle population.  Global Change Biology: 13(923-932)

Spotila, James R. 2004. Sea Turtles: A Complete Guide to Their Biology, Behavior, and Conservation. The Johns Hopkins University Press.

Sea turtle’s nest is so egg-citing:  Sea turtle lays her eggs at Cape Henlopen in what may be the first such nesting here


Posted by Kristen S.
Kristen is a Fall, 2011 Intern at the National Marine Life Center. She recently graduated from U Mass Dartmouth with a degree in Marine Biology.


  1. Hi Meg.

    Thank you for your question, and for your interest in the effect of temperature changes in the ocean on sea turtles! It is an important topic and I’m glad you are researching it.

    Re 1: People at your school can help by working to reduce greenhouse gas emissions. There a lots of small, easy steps you can do. Change the lightbulbs to those that are energy efficient. Turn off lights and electronic equipment when not in use. Use energy efficient appliances and technology. Reduce, reuse, and recycle. Eliminate plastic as much as possible. Use reusable bags. Save water by taking shorter showers, turning off the faucet while brushing teeth and doing dishes, and using water efficient appliances.

    Re 2: There are many ways in which sea turtles will be affected by climate change. Probably two of the most significant are the potential change in sex ratio and the reduction of nesting habitat.
    – The sex of a hatchling turtle is determined by the temperature at which it incubates. Eggs incubating at cooler temperatures turn into male turtles. Eggs incubating at warmer temperatures turn into female turtles. The change in the sex ratio of the nests caused by warmer temperatures can skew the population and lead to population decline.
    – With climate change and overall global warming comes the melting of the polar ice caps and resulting sea level rise. Because so much of our coast line is developed and the beaches can’t move back to accommodate the rising oceans, beach habitat will decline. It will become harder and harder for sea turtle females to find suitable beaches on which to build a nest and lay their eggs. More nests will be in danger of washing out. Fewer successful nests leads to fewer turtles and population decline.

    Re 3 – I have three favorite facts about sea turtles.
    – The fact that whether or not they develop into a female or male depends on the temperature at which they incubate.
    – The fact that they cannot pull their head and flippers inside their shell like terrestrial turtles can.
    – The fact that their natural history cycle makes them particularly vulnerable to human activity. If turtles are in decline, it’s a signal that the ecosystem is in decline. And, we can help!

    Plus, they are amazing animals. It’s a privilege to be able to help sick and injured turtles get well and be released back into the ocean.


  2. Hello,
    My name is Meg and I am researching the effect of temperature changes in the ocean on sea turtles and was wondering if I could ask a couple questions?

    What can people at my school do to help?
    What are the most important things to know about the sea turtles being effected by the temperature change?
    What is your favorite fact about the sea turtles?

    Thank you,

  3. Sea turtles are very weird.

  4. Wow! Thanks for writing this up. This is a topic I’ve been wanting to do research on myself! I’ve known about temperature dependent sex determination for a while – but the additional detail on how it works makes it so much clearer!

  5. Thank you for the information. It is frightening to thing about the impact of climate change on endangered species such as sea turtles.


  1. We Can Change Life A Lot: All Because of Sex-Determination – Biology 305 Summer 2016 - […] Temperature Effects on Sea Turtle Sex Ratios and the Potential Impact of Climate Change […]

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